Okay this might be related. When I went to my local bike shop I got a pair of plugs. But when I saw caps that were twisted, not like my regular round pop in type, I returned the plugs. After going back later, I was telling the guy who was working there about my problem. He told me that ducati has normal threaded plugs, but there is a nub that is a female piece that twists on top of the threaded plug to make it look like a normal plug. I didnt check it out myself though. If someone can aknowledge this, then the solution to your problem would be to get some female nub piecesfor your plugs.